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The effect of enzyme-inducing anticonvulsant drugs on the serum concentrations of lipoproteins has been widely studied. However, there is little agreement between the results with regard to the possible development of a lipoprotein profile related to an increased or decreased cardiovascular risk. It has been suggested that cholinesterase (ChE) could be induced by these drugs, something of undeniable interest as ChE appears to have a relation to the metabolism of lipoproteins. The serum activity of ChE was determined in a group of 90 adult epileptic patients (56 male and 34 female) treated with phenobarbital, phenytoin, and carbamazepine. The liver enzyme induction produced by these drugs was then evaluated by determining serum gamma-glutamyltranspherase activity and urinary excretion of D-glucaric acid. A significant increase of serum ChE (p < 0.005) was found in the group of patients compared to a control group (n = 49) with a similar distribution for age and sex. A significant correlation was found for both male and female patients between ChE and concentrations of triglycerides, phospholipids, cholesterol, low-density lipoprotein (LDL) phospholipids, LDL-cholesterol, and apolipoprotein B (p < 0.01). Similarly, in female patients, ChE had a significant correlation with the total cholesterol/high-density lipoprotein (HDL) cholesterol and LDL-cholesterol/HDL-cholesterol ratios (p < 0.01). The ChE/HDL-cholesterol relationship, which has been proposed as a marker for cardiovascular risk, presented significant correlations with the total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratios in patients of both sexes (p < 0.001). In the case of epileptic patients treated with enzyme-inducing anticonvulsant drugs, there may be an association between the possible induction of ChE and the metabolism of lipoproteins containing apolipoprotein B. [ABSTRACT FROM AUTHOR]

Background: It has recently been reported that patient selection has a strong impact on the agreement between glomerular filtration rate (GFR) estimates from serum cystatin C and creatinine. The aim of our study was to evaluate the effect of creatinine production rate (CPR) on this subject., Material and Methods: GFR was estimated from serum cystatin C and from creatinine using the 4- and 6-variable Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in 50 healthy subjects, 43 patients with renal failure, 794 kidney and 104 liver transplant recipients, 61 patients with heart failure, 59 patients with biliary obstruction, and 113 critically ill patients., Results: In the 295 patients with impaired CPR (< 900 mg/24 h/1.73 m(2)), discordances of more than 40% between GFR(MDRD4) and GFR(cystatinC) were observed in 38% of cases, between GFR(MDRD6) and GFR(cystatinC) in 22%, and between GFR(CKD-EPI) and GFR(cystatinC) in 27% (in all cases due to GFR overestimation from creatinine). In the 929 patients with maintained CPR (> 900 mg/24 h/1.73 m(2)), greater discordances than 40% between GFR(MDRD4) and GFR(cystatinC) were observed in 8% of cases, between GFR(MDRD6) and GFR(cystatinC) in 9%, and between GFR(CKD-EPI) and GFR(cystatinC) in 7% (in the major part of cases due to GFR overestimation from cystatin C)., Conclusion: The main source of differences of more than 40% between GFR estimates from serum creatinine and cystatin C is a GFR overestimation in patients with low CPR and GFR underestimation in patients with high CPR by the creatinine-derived equations.

Background: Pro-inflammatory cytokine production is directly inhibited by acetylcholine (ACh), and a relationship between total circulating ACh hydrolytic capacity and inflammatory reactions has been previously reported. Butyrylcholinesterase (BChE) is the major ACh hydrolyzing enzyme in plasma, and the aim of our study was to evaluate its association with low-grade systemic inflammation., Material and Methods: A total of 4,077 patients clinically managed in the Cardiology, Hypertension, and Digestive Medicine Units were included in our study. Three subclinical chronic inflammatory degrees were established in accordance with the high-sensitivity C-reactive protein (hsCRP) concentrations proposed, for low (< 1 mg/L), average (1-3 mg/L), and high (> 3-10 mg/L) cardiovascular disease risk estimation., Results: In male patients with subclinical chronic inflammation and hsCRP concentrations < 1 mg/L, a significant positive correlation was observed between BChE and hsCRP (p < 0.02); however, for hsCRP concentrations > 3 mg/L, the correlation between these variables in both sexes becomes significantly negative (p < 0.001), as in patients with acute inflammation (hsCRP > 10 mg/L). In all cases significant positive correlations were obtained between the BChE activities and albumin concentrations (p < 0.001)., Conclusions: The liver production of BChE and albumin occurs in a coupled fashion, and these biochemical variables may be considered as negative inflammatory reactants, whose serum levels are inversely associated with the increasing degree of subclinical inflammation.

Background: There is significant immunoassay cross-reactivity between everolimus and sirolimus, and their routine determination using a common method may reduce the reagent costs., Methods: In 122 blood samples from kidney (n = 30) and liver (n = 92) transplant recipients, everolimus concentrations were determined using the Abbott IMx® microparticle enzyme immunoassay (MEIA) as previously described, and the Abbott sirolimus chemiluminescence magnetic microparticle immunoassay (CMIA) on the Architect-i1000® system., Results: A high correlation coefficient (r = 0.981, p < 0.001) and a linear regression MEIA = 0.73CMIA + 0.55, with an acceptable standard error of the estimate (ma68 = 0.32 ng/mL), were obtained, indicating the transferability of the results produced by both immunoassays., Conclusions: The newly-developed sirolimus CMIA assay on the Architect® platform may be a valid alternative to other immunoassays for the routine therapeutic monitoring of everolimus.

Background: Valproic acid (VPA) apparent clearance (CL) estimated from total serum concentrations is analogous in elderly and non-elderly adult patients. As drug-protein binding decreases in old age, the aim of our study was to evaluate the confounding effect of the serum albumin concentration on the VPA apparent CL in elderly patients., Methods: In 102 epileptic out-patients treated with VPA in monotherapy, serum total steady-state trough concentrations (Css) were determined. Css concentrations were normalized for a 42 g/L albumin concentration (Css(N)), and the apparent CL and normalized apparent CL(N) were calculated., Results: A poor concordance of 53% was found in the classification of Css and Css(N) levels of VPA as subtherapeutic, therapeutic, or supratherapeutic dose. In the elderly (≥65 years) and non-elderly adult patients, the VPA apparent CL was similar; however, normalized apparent CL(N) was significantly lower in older patients (P < 0.01), with a 40% median decrease., Conclusions: Total VPA concentrations should be interpreted with caution, mainly in older patients, in which determination of unbound or normalized total drug concentrations may be clinically useful. Normalization of total concentrations permits an estimation of the masking effect of serum albumin concentrations on the VPA apparent CL in elderly patients.

Background: Although the possible interference of digoxin-like immunoreactive substances (DLIS) on the Architect iDigoxin chemiluminiscent microparticle immunoassay (CMIA) has been emphasized by the manufacturer, a specific study about this subject has still not been carried out., Methods: Apparent serum digoxin concentrations were determined using the Architect iDigoxin CMIA from Abbott Laboratories in digoxin-free pregnant women (n = 50), and patients with liver disease (n = 50), renal insufficiency (n = 50), kidney (n = 25) or liver (n = 25) transplant, and critical illness (n = 50)., Results: In all of the patients included in this study, apparent serum digoxin concentrations were lower than the correspondent quantification limit (< 0.30 microg/L)., Conclusions: The Architect iDigoxin CMIA assay would be relatively free from endogenous DLIS positive interferences.

Background: Recently, the use of the truncated area under the curve from 0 to 2 h (AUC(0-2)) of mycophenolic acid (MPA) has been proposed for therapeutic monitoring in liver transplant recipients. The aim of our study was the evaluation of the clinical usefulness of truncated AUC(0-2) in kidney transplant patients., Methods: Plasma MPA was measured in samples taken before the morning dose of mycophenolate mofetil, and one-half and 2 h post-dose, completing 63 MPA concentration-time profiles from 40 adult kidney transplant recipients. The AUC from 0 to 12 h (AUC(0-12)) was calculated using the validated algorithm of Pawinski et al. The truncated AUC(0-2) was calculated using the linear trapezoidal rule, and extrapolated to 0-12 h (trapezoidal extrapolated AUC(0-12)) as previously described., Results: Algorithm calculated and trapezoidal extrapolated AUC(0-12) values showed high correlation (r=0.995) and acceptable dispersion (ma68=0.71 μg·h/mL), median prediction error (6.6%) and median absolute prediction error (12.6%). The truncated AUC(0-2) had acceptable diagnostic efficiency (87%) in the classification of subtherapeutic, therapeutic or supratherapeutic values with respect to AUC(0-12). However, due to the high inter-individual variation of the drug absorption-rate, the dispersion between both pharmacokinetic variables (ma68=6.9 μg·h/mL) was unacceptable., Conclusions: The substantial dispersion between truncated AUC(0-2) and AUC(0-12) values may be a serious objection for the routine use of MPA AUC(0-2) in clinical practice.

Background: Patients treated with valproic acid (VPA) present a high incidence of non-alcoholic fatty liver disease (NAFLD) (around 61%). Several recent studies suggest that low copper stores could be associated with NAFLD, and a significant decrease of copper availability in VPA-treated patients has been described., Design and Methods: In 101 adult epileptic patients treated with valproic acid in monotherapy (n = 75) and polytherapy (n = 26) the copper availability was evaluated using the specific oxidase activity of ceruloplasmin (activity per unit mass of enzyme protein) and the copper/ceruloplasmin ratio. Copper deficiency was supposed in the cases in which this biochemical variable was smaller than the lower reference limit (333 U/g)., Results: The differences between the groups of patients with ceruloplasmin oxidase activity smaller or greater than 333 U/g for the serum levels of aminotransferases, gamma-glutamyltransferase, butyrylcholinesterase, cholesterol, triglycerides, and C-reactive protein, and the APRI and FIB-4 liver fibrosis scores were not statistically significant. Most patients (93%) had low APRI and FIB-4 scores, suggesting absence of significant liver fibrosis., Conclusions: The results obtained do not confirm the hypothesis of an association between diminished copper availability and NAFLD in patients treated with valproic acid.

Objectives: Gastrointestinal side-effects caused by mycophenolic acid (MPA) are frequent in liver transplant recipients, and in these cases a switch from two to three daily doses is usually recommended. However, a limited sampling strategy for the estimation of MPA area under the curve from 0 to 8 hours (AUC(0-8h)) has not been made., Design and Methods: In 22 liver transplant patients who were administered MPA three times daily, the trapezoidal extrapolated MPA AUC(0-8h) values using a sampling time from 0 to 2 hours were calculated., Results: A tentative therapeutic range for MPA AUC(0-8h) of about 20-40 μg.h/mL is proposed, and in the 13 patients with supratherapeutic values the total leukocyte blood count was significantly lower than in the 9 patients with AUC(0-8h) ≤ 40 μg.h/mL (P < 0.001). Significant negative correlations were found between the total leukocyte blood count and the MPA trough levels (r = -0.458; P < 0.05), AUC(0-8h) (r = -0.479; P < 0.05), and AUC(0-2h) (r = -0.437; P < 0.05). A significant correlation was found between the trapezoidal extrapolated AUC(0-8h) and trapezoidal AUC(0-2h) results (r = 0.850; P < 0.001)., Conclusions: The trapezoidal extrapolated AUC(0-8h), and possibly trapezoidal AUC(0-2h), may be useful for routine therapeutic MPA monitoring in liver transplant recipients in which the dosing frequency is increased from twice to three times a day.

Background: The aim of our study was to evaluate the possible determination of everolimus concentrations using the newly-introduced sirolimus antibody conjugated magnetic immunoassay (ACMIA)., Methods: Everolimus concentrations were determined in 100 blood samples from kidney (n = 47) and liver (n = 53) transplant recipients using the IMx sirolimus microparticle enzyme immunoassay (MEIA) from Abbott as previously described (Clin Biochem 2007;40:132-36) and sirolimus ACMIA from Siemens Healthcare Diagnostics Ltd., Results: The ACMIA everolimus values were significantly higher than those of MEIA (p < 0.001). Analogous slope and intercept values were obtained in the linear regression between the ACMIA and MEIA results when compared to the Seradyn Certican everolimus controls or the blood samples from transplant recipients. Correction of the ACMIA values using the regression equation obtained for the control material (ACMIAcorrected = 0.55 ACMIA + 1.14) led to a satisfactory relationship with the results provided by the MEIA for the patients' samples (MEIA = 1.00 ACMIAcorrected + 0.30, r = 0.905, p < 0.001)., Conclusions: The sirolimus ACMIA on the Dimension platform, which does not require manual pre-treatment of the blood samples, may be an acceptable option for therapeutic everolimus monitoring, significantly reducing technician time in comparison to other widely-used immunoassays.

Background: Inappropriate doses and high serum concentrations of digoxin are highly prevalent in patients with renal impairment, and the drug dosage adjustment according to the glomerular filtration rate (GFR) is recommended. The aim of our study was to evaluate the dependence degree of digoxin total clearance (CL) on GFR, and the diagnostic efficiency of a predictive model for serum digoxin steady-state concentrations (Css) from estimated GFR by Cockcroft-Gault formula., Methods: In 400 outpatients treated orally with digoxin, serum Css were determined (fluorescence polarization immunoassay from Abbott Laboratories), and total CL was calculated. The prediction of Css was carried out using a hyperbolic model developed by Konishi et al in Japan (J Clin Pharm Ther 2002;27:257), and the constants of the equation were modified for a Caucasian population., Results: Only 26% of the digoxin CL interindividual variability may be explained by differences in GFR, and this fact is a serious limitation for the derived predictive models. A 65% diagnostic efficiency was obtained for original and modified hyperbolic models in the correct classification of predicted Css as subtherapeutic, therapeutic or supratherapeutic with respect to obtained Css concentrations., Conclusions: The diagnostic efficiency obtained in the prediction of serum digoxin concentrations from estimated GFR values is unacceptable for the drug dosage adjustment in clinical practice.

Background: In a patient with biliary obstruction, a macromolecular complex of cystatin C with liver plasma membrane fragments, which also contain several membrane-bound enzymes, which may be removed by butanol extraction, has recently been characterised. This could lead to an underestimation of the glomerular filtration rate (GFR) from serum cystatin C concentration., Methods: Using the particle enhanced nephelometric immunoassay (PENIA), serum cystatin C concentration was determined in 50 healthy controls, 43 patients with renal insufficiency, 68 kidney and 88 liver transplant recipients, and 60 patients with biliary obstruction. Residual cystatin C concentrations and gamma-glutamyltransferase (GGT) activities after butanol extraction were also determined., Results: In the controls and patients with renal insufficiency the residual concentrations of cystatin C after butanol extraction were always > or = 80%. However, in 2 renal and 7 liver transplant recipients and in 11 patients with biliary obstruction this biochemical variable was < 80%. A significant correlation between the residual cystatin C concentrations and residual GGT activities was obtained (r = 0.386, p < 0.001). In the relationship between estimated GFR from serum cystatin C and creatinine concentrations in the liver transplant recipients and patients with biliary obstruction, the 18 cases with residual cystatin C concentrations < 80% were included in the distribution of the total population data with no particular tendency., Conclusions: These results suggest that in the cases with residual cystatin C concentrations < 80% after butanol extraction, presumably due to the presence of circulating macromolecular cystatin C, the serum levels of cystatin C obtained using the PENIA assay do not lead to a systematic GFR underestimation.

Only two cases have been previously described about circulating endogenous antibodies interference on the immunochemical determination of digoxin. In an elderly patient with history of social cat handling was observed a moderate positive interference (about 0.8 ng/mL) on the Dimension® DGNA digoxin immunoassay (capture rabbit antibody), which was eliminated treating the serum samples with a heterophilic blocking reagent. The Architect® immunoassay was not affected., (Copyright © 2010 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.)

Objectives: In rats a significant increase of the copper biliary excretion is produced by valproic acid administration, however, a conclusive study on the possible appearance of copper deficiency in humans during treatment with this drug has still not been carried out., Design and Methods: In 101 adult epileptic patients treated in monotherapy (n=75) and polytherapy (n=26) with valproic acid, and 50 healthy controls, were determined serum copper, immunoreactive ceruloplasmin and its oxidase activity against o-dianisidine, in order to calculate the specific oxidase activity (activity per unit mass of enzyme protein) and copper/ceruloplasmin ratio., Results: Specific oxidase activity of ceruloplasmin and copper/ceruloplasmin ratio were significantly lower in the groups of patients treated with valproic acid than in the controls. Significant correlations were obtained between both biochemical variables (p<0001). In 38% of the patients treated in mono or polytherapy, the specific oxidase activities of ceruloplasmin were smaller than the estimated lower limit of reference., Conclusions: These results, possible due to a diminished copper content of the circulating ceruloplasmin, suggest that marginal or moderate copper deficiency may have a substantial prevalence among patients treated with valproic acid., (Copyright (c) 2010. Published by Elsevier Inc.)

Objectives: Therapeutic monitoring of sirolimus and everolimus is necessary in order to minimize adverse side-effects and to ensure effective immunosuppression. A sirolimus-dosing model using the concentration/dose ratio has been previously proposed for kidney transplant patients, and the aim of our study was the evaluation of this single model for the prediction of trough sirolimus and everolimus concentrations., Methods: Trough steady-state sirolimus concentrations were determined in several blood samples from each of 7 kidney and 9 liver maintenance transplant recipients, and everolimus concentrations from 20 kidney, 17 liver, and 3 kidney/liver maintenance transplant recipients. Predicted sirolimus and everolimus concentrations (Css), corresponding to the doses (D), were calculated using the measured concentrations (Css(0)) and corresponding doses (D(0)) on starting the study: Css = (Css(0))(D)/D(0)., Results: The diagnostic efficiency of the predicting model for the correct classification as subtherapeutic, therapeutic, and supratherapeutic values with respect to the experimentally obtained concentrations was 91.3% for sirolimus and 81.4% for everolimus in the kidney transplant patients. In the liver transplant patients the efficiency was 69.2% for sirolimus and 72.6% for everolimus, and in the kidney/liver transplant recipients the efficiency for everolimus was 67.9%., Conclusions: The model has an acceptable diagnostic efficiency (>80%) for the prediction of sirolimus and everolimus concentrations in kidney transplant recipients, but not in liver transplant recipients. However, considering the wide ranges found for the prediction error of sirolimus and everolimus concentrations, the clinical relevance of this dosing model is weak.

Objective: Various studies have revealed that mycophenolic acid (MPA) area under the time concentration curve (AUC) may have clinical value in mycophenolate mofetil dose adjustment. As the full AUC measurement is impractical in clinical practice, several abbreviated AUC profiles using pre-dose, and two or three post-dose samples have been proposed; however, the possible use of lower sampling time profiles has an unquestionable practical interest, and the aim of our study was the evaluation of several two-points algorithms using only one post-dose sample., Patients and Methods: In 60 MPA concentration-time profiles from 37 adult renal transplant patients treated with mycophenolate mofetil and concomitant tacrolimus, the MPA AUC values were estimated using the three sampling time algorithm (pre-dose, one-half and 2 h post-dose)of Pawinski et al. (Clinical Chemistry 48, 2002, 1497), trapezoidal extrapolated procedure according to Hale et al. (Clinical Pharmacology Therapeutics 64, 1998, 672), and two-points algorithm (pre-dose and 2 h post-dose) proposed by David-Neto et al. (Clinical Transplantation 19, 2005, 19)., Results: The AUC values estimated using the algorithm of Pawinski et al. had a very high correlation(r = 0.997, P < 0.001) with the trapezoidal extrapolated AUC results. The estimated AUC values obtained using the two-points algorithm of David-Neto et al. present a high correlation (r = 0.930, P < 0.001), acceptable mean prediction error (+3.3 +/- 1.8%), and a diagnostic efficiency of 94% in the classification of subtherapeutic, therapeutic, and supratherapeutic values, with respect to the three-points algorithm of Pawinskiet al., Conclusion: The two sampling time algorithm of David-Neto gave similar results to those of the three-sampling time algorithm of Pawinski, and both, with sampling over 2 h, may be useful for routine MPA AUC estimation in renal transplant recipients with concomitant tacrolimus. Both are unsuitable when unusually unpredictable pharmacokinetics are expected such as with entericcoated formulations.

The presence of endogenous antibodies in the serum of some patients has long been known to be a potential source of interference in immunoassays. We report falsely increased whole blood tacrolimus concentrations using the antibody conjugated magnetic immunoassay from Siemens HealthCare Diagnostics in a liver transplant recipient due to the presence of circulating endogenous antibodies (possibly heterophilic antibodies). Estimation of whole blood tacrolimus concentrations from the washed erythrocytes concentrations is proposed as a tentative approach for obtaining reliable results using the antibody conjugated magnetic immunoassay assay in these cases, leading to analogous blood tacrolimus concentrations to those produced by the microparticle enzyme immunoassay from Abbott Laboratories.

Background: Although high-performance liquid chromatography (HPLC) is the method of choice for blood sirolimus determination, the microparticle enzyme immunoassay (MEIA) run on the IMx analyser is widely used in therapeutic monitoring of this immunosuppressant agent. The aim of our study was to evaluate the possible determination of sirolimus using the fluorescence polarization immunoassay (FPIA) commercialized for everolimus quantification., Methods: Sirolimus concentrations were determined in whole-blood samples from liver and kidney transplant recipients using the Innofluor Certican FPIA (Seradyn Inc.) run on a TDx analyser (Abbott Laboratories), Sirolimus MEIA run on an IMx analyser (Abbott Laboratories), and HPLC (UV detection) methods., Results: The Innofluor FPIA has a similar cross-reactivity with everolimus and sirolimus, and the within- and between-run coefficients of variation obtained for sirolimus determination were 2.7%-13.3%. In analysing different blood samples from liver and kidney transplant patients the linear regressions obtained were: FPIA = 1.12 HPLC + 0.43 (n=104, r=0.874), MEIA = 1.14 HPLC (n=146, r=0.892), and FPIA = 1.00 MEIA + 0.29 (n=106, r=0.941). Better correlation coefficients were obtained between the methods in the liver transplant samples (r>or=0.900) than in the kidney transplant samples (r>or=0.849). No significant effect was found for sirolimus clearance or the blood hematocrit on the relationship between the results produced by both immunoassays and HPLC., Conclusion: The Innofluor FPIA is a valid alternative with an analogous performance to the MEIA for the therapeutic monitoring of sirolimus.

Objective: The aim of this study was to compare the estimated glomerular filtration rate (GFR) using the Cockcroft-Gault and the 4-, 5-, and 6-variable Modification of Diet in Renal Disease (MDRD) formulas for digoxin dose adjustment., Methods: Steady-state serum digoxin concentrations were determined in 100 patients with heart failure and normal to severely impaired renal function. Total clearance (CL) and predicted average concentrations of digoxin were calculated using general pharmacokinetic principles., Results: The mean+/-SEM (median) estimated GFR values were 48.9+/-2.8 (46.5) mL/min/1.73 m(2) using the Cockcroft-Gault formula, 61.4+/-3.6 (56.4) mL/min/1.73 m(2) using the MDRD4 formula, 56.8+/-3.3 (52.1) mL/min/1.73 m(2) using the MDRD5 formula, and 53.3+/-3.0 (48.7) mL/min/1.73 m(2) using the MDRD6 formula, with high correlation coefficients between the estimates (r > or = 0.928, P < 0.001). Significant correlations were found between the digoxin total CL and estimated GFR by the Cockcroft-Gault (r = 0.649, P < 0.001), MDRD4 (r = 0.634, P <0.001), MDRD5 (r = 0.635, P < 0.001), and MDRD6 (r = 0.652, P < 0.001) formulas. A significant negative correlation of the digoxin total CL/GFR ratio with estimated GFR was obtained (r = -0.356, P < 0.001), with a high variability for this ratio for GFR lower than 60 mL/min. Analogous correlation coefficients were found between the obtained and predicted digoxin concentrations calculated using the estimated GFR by the Cockcroft-Gault (r = 0.628, P < 0.001), MDRD4 (r = 0.642, P < 0.001), MDRD5 (r = 0.650, P < 0.001), and MDRD6 (r = 0.665, P < 0.001) formulas, with a wide dispersion between the values in all cases., Conclusion: For GFR lower than 60 mL/min, the high interindividual variation of the digoxin total CL found among patients with similar renal function is an important limiting factor in the prediction of digoxin dosage regimens.

Objectives: The use of new antipsychotic drugs is associated with an increased risk of diabetes and metabolic syndrome, and the routine monitoring of blood lipids during treatment has been recommended. Recently, a new formula for the estimation of low-density lipoprotein (LDL) cholesterol from total cholesterol and triglycerides has been proposed by Anandaraja et al. (Int J Cardiol 2005; 102: 117), and the aim of our study was its evaluation in schizophrenic patients treated with antipsychotic drugs., Materials and Methods: In 487 serum samples from schizophrenic patients treated with clozapine in polytherapy, the concentrations of LDL cholesterol were determined by agar gel electrophoresis and the formula of Friedewald et al. (Clin Chem 1972; 18: 499), and compared with the results of the Anandaraja's formula., Results: A higher correlation and lower error of the estimate of the electrophoresis results was found with those of Friedewald (r=0.940, ma68=0.17 mmol/L) than those of Anandaraja (r=0.811, ma68=0.31 mmol/L). Similar results were obtained on making a dichotomy of the patients with and without metabolic syndrome lipid profile. A highly significant correlation was found between the high-density lipoprotein (HDL) cholesterol levels and the Anandaraja/Electrophoresis (r=0.817, p<0.001) and Anandaraja/Friedewald (r=0.977, p<0.001) ratios., Conclusions: According to our data, Anandaraja's formula tends towards an overestimation or underestimation of LDL cholesterol levels, depending on whether the HDL cholesterol levels are high or low, which may be clinically significant. These results do not support the proposed better accuracy of the Anandaraja's than the Friedewald's formula.

Objective: Therapeutic drug monitoring of clozapine may be useful for the clinical management of schizophrenic patients treated with this atypical antipsychotic drug. The aim of our study was the evaluation of three models for the prediction of steady-state trough clozapine concentration., Patients and Methods: The trough serum concentrations of clozapine and norclozapine were determined by high-performance liquid chromatography in 296 samples from a group of 21 schizophrenic patients selected for their good therapeutic compliance. Also, the predicted clozapine concentrations were estimated by applying the models of Oyewumi et al. (Ther Drug Monit 1995; 17: 137), Perry et al. (Biol Psychiatry 1998; 44: 733) and Rostami-Hodjegan et al. (J Clin Psychopharmacol 2004; 24: 70)., Results: The efficiency for the accurate estimation of clozapine concentrations as subtherapeutic (<240 ng/mL), therapeutic (240-750 ng/mL) or supratherapeutic (>750 ng/mL), using the models of Oyewumi et al., Perry et al., and Rostami-Hodjegan et al., was 82%, 71% and 77% respectively., Conclusions: The predictive model of Oyewumi et al., which shows an easy calculation way and the greater diagnostic efficiency, may be of clinical value for the prediction of clozapine concentration or the dose required to achieve a specified concentration.

At present, the determination of steady-state trough serum/plasma concentrations of clozapine is considered a useful tool for the clinical management of schizophrenic patients treated with this drug. In a previously published study, it was indicated that only plasma should be used to avoid a significant underestimation of clozapine and norclozapine concentrations; however, a formal evaluation of this topic has still not been made, and a consensus on the use of plasma or serum for therapeutic clozapine monitoring may be desirable. Paired samples of serum and plasma (K3EDTA solution contained in Vacutainer tubes) were obtained from 40 schizophrenic patients, and clozapine and norclozapine concentrations were determined by high-performance liquid chromatography. For the parent drug and its metabolite, serum concentrations were higher than in plasma (approximately 7%), although the correction of plasma concentrations in function of hematocrit values reduced this difference to 3%. High correlation coefficients were found between the serum and uncorrected or corrected plasma clozapine concentrations (r = 0.996, P < 0.001), with clinically acceptable differences between the means and standard error of the estimate and consequently with transferability of the results. The clozapine and norclozapine concentrations in five lithium heparin-containing plasma samples (371.9 +/- 226.7 ng/mL and 217.9 +/- 113.1 ng/mL) were analogous to the corresponding hematocrit-corrected EDTA-containing plasma values (374.4 +/- 225.4 ng/mL and 223.5 +/- 115.2 ng/mL), with correlation coefficients of r > or = 0.998 (P < 0.001). Serum or plasma samples may be used for the therapeutic monitoring of clozapine, and no practical advantages have been found with regard to the stability of the drug or imprecision obtained by using either type of biological matrix.

Background: The proposed action mechanism and pharmacological activity of carbamazepine (CBZ) and its major metabolite, carbamazepine-10,11-epoxide (CBZE), are the same. The aim of our study was the investigation of the effect of concomitant antiepileptic treatment and renal insufficiency on the relative proportions of serum CBZ and CBZE., Methods: Serum trough steady-state CBZ and CBZE concentrations were determined by high-performance liquid chromatography (HPLC) in 140 epileptic patients treated with CBZ in monotherapy (n=100) and polytherapy with phenytoin, phenobarbital and valproate (n=40). The levels of CBZ were also determined using the Dade Behring enzyme multiplied immunoassay technique (EMIT). The glomerular filtration rate (GFR) was estimated from serum cystatin C using the Dade Behring nephelometric immunoassay., Results: The CBZE/CBZ and CBZ+CBZE/CBZEMIT ratios were significantly increased in 7 cases (3 in monotherapy and 4 in polytherapy) with GFR<60 mL/min/1.73m2 in relation to the patients treated in monotherapy or polytherapy having normal or mildly decreased renal function (p<0.001)., Conclusions: In patients with moderate to severe renal insufficiency the relative proportion of CBZE with respect to the parent drug is significantly increased. In these cases, the CBZ concentrations obtained using the EMIT, or other immunoassays having low CBZE cross-reactivity, may have an inadequate diagnostic efficiency.

Background: Published data on the performance of the new Dade Behring antibody conjugated magnetic immunoassay (ACMIA) for tacrolimus determination are scarce. The aim of this study was to compare the results obtained using the ACMIA and Abbott microparticle enzyme immunoassay (MEIA), which is the most widely used method for therapeutic tacrolimus monitoring., Methods: Trough tacrolimus concentrations were determined in 305 blood samples from kidney (n=138) and liver (n=167) transplant recipients using the ACMIA and MEIA immunoassays. The MEIA results were corrected for hematocrit values lesser than 30% and higher than 40% (Hermida et al. Clin Lab 2005; 51: 43-45)., Results: The obtained ACMIA within- and between-run variation coefficients (<10.8%) were acceptable. In the comparison between ACMIA and MEIA results in the blood samples studied, the regression equation was: ACMIA=1.02MEIA+0.29 (r=0.912, p<0.001), with an acceptable difference between the means (8.13+/-0.53 ng/mL vs. 7.62+/-0.50 ng/mL). However, in accordance with the well-established interference of the hematocrit on the MEIA results, a highly significant negative correlation between the MEIA/ACMIA ratio and the hematocrit values was obtained (r=-0.585, p<0.001). When the MEIA results were corrected according to the hematocrit (MEIAHtC), the regression with ACMIA levels was: ACMIA=1.08MEIAHtC-0.09 (r=0.926, p<0.001). This equation was analogous to that obtained between ACMIA and MEIA tacrolimus concentrations in the 164 blood samples with hematocrit of 30-40%., Conclusions: ACMIA is an acceptable option for therapeutic tacrolimus monitoring, with an important decrease in technician time in relation to the widely used MEIA.

Background: Carbamazepine (CBZ) occasionally causes haematological disorders such as thrombocytopenia, and recently a case of oxcarbazepine (OXCBZ)-induced thrombocytopenia has been described. The aim of our study was blood platelet count determination in epileptic patients treated with CBZ and OXCBZ, and its relationship with the dose and serum levels of these drugs and its metabolites., Methods: The serum levels of CBZ and its epoxide, and the pharmacologically active monohydroxy derivative of OXCBZ were determined in 137 patients treated with CBZ, and 60 patients treated with OXCBZ. The platelet count, mean platelet volume, and platelet size distribution width were also determined., Results: The difference between the platelet counts of the patient groups treated with CBZ and OXCBZ was not significant. No significant correlations between the platelet count and serum levels of the administered antiepileptic drugs and their metabolites were found. However, significant negative correlations between the platelet count and the daily doses of CBZ and OXCBZ were obtained (p<0.01). In 5 cases (4 treated with CBZ and 1 with OXCBZ) the platelet count was <150 x 10(9)/l., Conclusions: In accordance with the mean platelet volume and platelet distribution width, the thrombocytopenia observed in some of the patients studied was due to a hyper-destruction of peripheral blood platelets. However, the results obtained suggest that the mechanism of CBZ or OXCBZ-induced thrombocytopenia is not due to a direct toxicity of these drugs or their major metabolites on the circulating platelets. Although, the patients treated with OXCBZ shown a lower prevalence for thrombocytopenia (1.7%) than those treated with CBZ (2.9%), the routine platelet count monitoring in patients treated with both drugs may be recommended.

Several factors have been considered in relation to the free radical formation in schizophrenia, such as the disease itself, drug treatment and smoking. Several chemicals and drugs may cause damage to the renal tubules by different subcellular mechanisms including oxidative stress, and the aim of our study was the investigation of tubular dysfunction in schizophrenic patients. The urinary excretion of beta-N-acetylhexosaminidase (Hex) and its isoenzymes Hex A and Hex B, alpha1-microglobulin, albumin, total proteins and fractionated porphyrins were determined in 45 schizophrenic patients treated with first- and second-generation antipsychotics. In 7 patients, an increase in proteinuria of tubular origin was found, and in one as a result of mixed glomerular/tubular origin. The group of patients had a significantly higher level of excretion than the control group (n = 54) of total Hex (p < 0.001), Hex A (p < 0.05), Hex B (p < 0.001) and the relative proportion of this isoenzyme (p < 0.001). In some cases with normal levels of total Hex and urinary alpha1-microglobulin, the proportion of Hex B was already increased. Significant correlations were found for total Hex and its isoenzymes with alpha1-microglobulin (p < 0.001). Also, the porphyrins had significant correlations with total Hex (p < 0.001), Hex A (p < 0.05), Hex B (p < 0.005) and alpha1-microglobulin (p < 0.001). In the group of patients studied, it was possible to reveal early tubular cell damage (affected structural integrity) with increased excretion of Hex B, possibly mediated by free radicals, previous to the decrease in tubular reabsorption of proteins with low molecular mass filtered by the glomerulus (affected functional integrity).

Chitotriosidase (ChT) is mainly secreted by monocyte-derived macrophages, and is considered a useful marker of macrophage activation. Macrophages represent the first line of defence against Mycobacterium tuberculosis, and consequently the study of ChT activity in pleural effusions (PE) would be of clinical value in the laboratory characterization of tuberculous pleurisy. ChT and adenosine deaminase (ADA) activities were determined in 12 tuberculous PE, 26 non-tuberculous lymphocytic PE and 25 neutrophilic PE. The enzyme heterogeneity study for ChT was made by thermal inactivation at 60 degrees C according to Wajner et al. (Clin Biochem 2004;37:893). ChT activity was significantly higher in the group of tuberculous PE than in the non-tuberculous lymphocytic PE group (p < 0.01), although no significant difference was found with respect to neutrophilic PE. The correlation between ChT and ADA was statistically significant, although in the partial correlation keeping the protein concentration constant, statistical significance was only achieved in tuberculous and non-tuberculous lymphocytic PE (r = 0.358, p < 0.05). In lymphocytic PE, a ChT activity greater than 40 mmol/h/mL has a sensitivity of 92%, specificity of 72%, and efficiency of 78% for the biochemical characterization of tuberculous pleurisy. Residual activities obtained for ChT by heat inactivation did not make it possible to differentiate the enzyme isoforms in PE presumably secreted by macrophages and polymorphonuclear leukocytes.

The Abbott microparticle enzyme immunoassay (MEIA) and the Dade Behring enzyme multiplied immunoassay technique (EMIT) are the most frequently used methods in the therapeutic drug monitoring of tacrolimus; however, a hematocrit-dependent interference for the MEIA has been described. In 244 whole blood samples from patients with liver (n=152) and kidney (n=92) transplants, the MEIA/EMIT ratio presented a highly significant negative correlation with the hematocrit (r = -0.482, p < 0.001). On distributing the samples into three groups with a hematocrit of less than 30%, 30-40%, and higher than 40%, different regression equations were found between the results of MEIA and EMIT and demonstrate the different effect of the hematocrit on both immunoassays. Correcting the MEIA results by calculation for a hematocrit of less than 30% and higher than 40% (Hermida et al. Clin Lab 2005; 51: 43-45) led to a regression with EMIT that was similar to that found between MEIA and EMIT for the group of samples with a hematocrit of 30-40%. Furthermore, the corrected MEIA/EMIT ratio had a poor correlation with the hematocrit (r = 0.149, p < 0.05). In 95 samples with a hematocrit of less than 25% (n=73) and higher than 40% (n=22) we also determined the tacrolimus levels using the modified MEIA method to correct hematocrit interference, as proposed by Tomita et al. (Ther Drug Monit 2005; 27: 94-97). In the samples with a hematocrit of less than 25%, correcting the MEIA results by calculation produced results that were similar and had a high correlation coefficient (r = 0.954, p < 0.001) to those of the modified MEIA method, whose application as a routine practice is more expensive and laborious. Calculation of the corrected MEIA values in anemic patients may be useful for the therapeutic monitoring of tacrolimus.

Objectives: Everolimus (Certican) is a new immunosuppressant derived from sirolimus (Rapamune) with a 2-hydroxyethyl chain at position 40 of the macrolide ring. The aim of our study was to evaluate the possible determination of everolimus in whole blood using a commercialized microparticle enzyme immunoassay for sirolimus determination., Design and Methods: Everolimus concentrations were determined in blood samples from 11 kidney transplant patients (n=51) and different control materials (n=35) using the Seradyn Innofluor Certican fluorescence polarization immunoassay (FPIA) and the Abbott IMx sirolimus microparticle enzyme immunoassay (MEIA)., Results: The MEIA gave a concentration-dependent cross-reactivity with the everolimus, with a linear regression between the assigned values (y) for the Innofluor Certican calibrators and those obtained (x) using this immunoassay: y=0.96x+0.67 (ma68=0.21 microg/L, r=0.974, p<0.001). The within- and between-run coefficients of variation using the MEIA were

The debate continues regarding the possible interference of phenytoin metabolites in phenytoin immunoassays, and its clinical importance for patients with renal failure. The aim of this study was to compare the results obtained using the Abbott fluorescence polarization immunoassay (FPIA), Dade enzyme-multiplied immunoassay technique (EMIT), and high-performance liquid chromatography (HPLC) to establish the significance of the differences in conditions of renal failure. Thirty-six adult patients who had been treated with phenytoin and whose renal function ranged from normal to severely impaired were chosen for this study. In accordance with previously established validation criteria for analytical methods for the determination of drugs, a 15% bias from the HPLC phenytoin values was considered an acceptable limit. The mean (+/-SEM) glomerular filtration rate (GFR) of the patients was 37.5+/-4.6 mL/min (range = 10-102 mL/min). The mean values found using FPIA (10.8+/-1.2 microg/mL) and EMIT (10.8+/-1.3 microg/mL) presented acceptable deviations with respect to HPLC (10.5+/-1.2 microg/mL), and a high correlation was found among the results (N = 36) of the different methods (r > or = 0.987, P < 0.001). An FPIA deviation above the 15% bias limit with respect to HPLC was found only in two cases with very low serum phenytoin concentrations and low GFR values (< 20 mL/min), although it does not appear to be important in terms of adjusting drug dosage. According to our data, FPIA and EMIT gave accurate results for total phenytoin in serum samples from patients with renal failure., (2007 Wiley-Liss, Inc.)

Background: ss-N-acetylhexosaminidase (Hex) is a lysosomal hydrolase, whose determination in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) has provided discordant results., Methods: Total Hex and its isoenzymes Hex A and Hex B were determined using a thermodynamic procedure in the CSF of 27 patients with definitive MS, 8 with possible MS, 9 with meningitis, 14 with other neurological diseases, and in 10 controls without any neurological disease., Results: In the group of patients with definitive MS, the total Hex and Hex A were significantly higher than in the control group (p<0.001), with a possible association of greater enzymatic activities with the presence of oligoclonal bands and recent relapse; however, an overlap was detected for the activities of total Hex and its isoenzymes between the groups of patients with different neurological diseases. A significant correlation was obtained for neuron-specific enolase (NSE) with total Hex and Hex A and Hex B isoenzymes (p<0.001); however, in the partial correlation statistical significance was only obtained between NSE and Hex A (p<0.001) which is the most abundant Hex isoenzyme in the brain., Conclusions: Although the inflammatory process in MS mainly takes place in the perivascular zone, with little activity in the cerebral parenchyma, the significant increase of NSE and Hex A isoenzyme in CSF reveals a neuronal damage. The disease status may have effect on the CSF Hex activity.

Dosage regimes of aminoglycosides and vancomycin are modified according to the glomerular filtration rate (GFR). In 130 hospitalized patients who were administered amikacin, gentamicin, tobramycin, and vancomycin by intermittent intravenous infusion, we compared the predicted GFR values from the serum concentrations of creatinine (Cockcroft and Gault. Nephron. 1976;16:31-41) and cystatin C (Larsson et al. Scand J Clin Lab Invest. 2004;64:25-30) with respect to their relevance for proper dosage. In 83% and 67% of the cases, respectively, the serum levels of albumin and cholinesterase were below the corresponding lower limit of the reference range. The ratio of creatinine/cystatin C concentrations presented significant correlations with the predicted rate of creatinine production (r=0.762, P<0.001), serum albumin concentration (r=0.205, P<0.05), and catalytic serum concentrations of cholinesterase (r=0.207, P<0.05), gamma glutamyltransferase (r=-0.273, P<0.01), and alkaline phosphatase (r=-0.289, P<0.01). The GFR (mean+/-SD; median) predicted by the serum creatinine (84.0+/-35.1 mL/min/1.73 m; 82.6 mL/min/1.73 m) was significantly higher (P<0.001) than that predicted by the serum cystatin C (53.1+/-30.2 mL/min/1.73 m; 44.9 mL/min/1.73 m). The ratio between the GFR values predicted by creatinine and cystatin C had a highly significant negative correlation with the rate of creatinine production (r=-0.912, P<0.001). Furthermore, significant differences were found for the peak concentrations and clearances of amikacin and vancomycin estimated by means of the Abbottbase Pharmacokinetic Systems program, and using the GFR values predicted by the serum creatinine and cystatin C (P<0.005). In patients with hepatic dysfunction, the clearance of creatinine predicted by the Cockcroft-Gault formula leads to a significant overestimation of the GFR. Cystatin C seems to be a valid alternative as a GFR marker with regard to drug dose adjustment in these cases.

Determination of the glomerular filtration rate (GFR) is important for the drug dosage adjustment and clinical management of patients. The aim of our study was the comparison of estimated GFR values from serum creatinine (eGFRcreatinine) and cystatin C (eGFRcystatin C) in patients with impaired creatinine production. A total of 564 serum samples from patients with kidney disease (n=179), liver (n=71) and kidney (n=182) transplants, critically ill patients (n=82) and healthy subjects (n=50) were analyzed for serum creatinine and cystatin C. The creatinine production rate (CPR) was significantly lower in the different groups of patients than in the control group (p<0.001). A negative correlation was found between the eGFRcreatinine/eGFRcystatin C ratio and CPR (r= -0.964, p<0.001). For CPR higher than 800 mg/24h both procedures for estimating the GFR classified values higher and lower than 60 mL/min with an acceptable agreement; however, for CPR less than 800 mg/24h the eGFRcreatinine led to false negatives in a high number of cases with eGFRcystatin C <60 mL/min.

The action of some anticonvulsant drugs as the causal agents of attacks of acute porphyria has been widely documented in the literature. However, little attention has been paid to the effect of these drugs on the urinary excretion of porphyrins in non-porphyric subjects. In a sample of 82 epileptic patients treated with phenobarbital (n = 54), phenytoin (n = 64), carbamazepine (n = 33), and valproate (n = 8), the daily doses were expressed according to a drug score that would reflect the capacity of these drugs as enzymatic inducers when administered in polytherapy. A significantly increased urinary excretion of D-glucaric acid (DGA) and porphyrins was found in this group of patients (P<0.001), with coproporphyrin being the major fraction in all cases (>60%). Urinary DGA had a highly significant correlation with the drug score (r = 0.783, P<0.001); however, no significant correlations were found between the urinary porphyrins and DGA (r = 0.005) or the drug score (r = 0.053). Neither was any significant relationship found between the urinary porphyrins and the serum activity of 5'-nucleotidase (r = 0.066) or the presence of a cholestasis objectivized through the presence of the isoform of gamma-glutamyltransferase with beta-globulins electrophoretic mobility. However, in a group of 10 patients a significant correlation was found between the urinary excretion of porphyrins and beta-N-acetylhexosaminidase (r = 0.790, P<0.01). Therefore, it does not appear that the liver enzyme induction, or even a subclinical cholestasis, produced by the antiepileptic drugs administered to these patients may serve to explain the increase in the urinary excretion of porphyrins. A possible renal origin is proposed for the increase of urinary porphyrins in these cases.

Objectives: The relative proportion in percentage of the isoenzyme A of beta-hexosaminidase (Hex) is the single discriminatory function most frequently used for the biochemical screening of heterozygote Tay-Sachs disease carriers. It has been suggested that the assay of the Hex isoenzymes in homogeneous cell preparations is preferable to that in mixed total leukocytes which present greater interindividual variation. The major aim of our study was the evaluation of this hypothesis., Design and Methods: Total Hex and its Hex A and Hex B isoenzymes were determined in different samples of serum and plasma (n = 81) as well as in lysates of platelets (n = 75), and mononuclear (n = 81), polymorphonuclear (n = 81) and mixed total leukocytes (n = 33)., Results: The interindividual variations found for % Hex A in the different biological samples were: plasma (CV = 23.4%), platelets (CV = 10.2%), mononuclear (CV = 5.7%), polymorphonuclear (CV = 5.3%) and total leukocytes (CV = 7.1%). Although the relative proportion of Hex A was significantly greater in polymorphonuclear than in mononuclear leukocytes (P < 0.001), a statistical significance was not attained for the correlation between the relative proportions of blood polymorphonuclear cells and Hex A in mixed total leukocytes (r = 0.220)., Conclusions: The use of total leukocyte lysates does not appear to introduce a significant increase for the interindividual variation of the Hex A isoenzyme relative proportion in relation to the use of homogeneous cell preparations.

Background: The relationship between the progress of tubular damage and renal insufficiency in autosomal-dominant polycystic kidney disease (ADPKD) is a subject of doubtless interest, and is the object of this present work., Methods: A total of 92 adult ADPKD patients of both genders were studied, none of which presented end-stage renal disease (ESRD), and classified according to an ultrasound score based on kidney size and number of cysts. Urinary albumin and beta-N-acetylhexosaminidase (Hex) and its isoenzymes were determined, together with serum glutathione peroxidase, cystatin C, creatinine, and urea., Results: A frequent elevation of the urinary Hex was found and an alteration of its isoenzymatic profile, with 31% of the normotensive patients with normoalbuminuria already presenting an increased proportion of Hex B isoenzyme. Keeping age constant, a partial significant correlation was found between the ultrasound score and the proportion of Hex B (r = 0.352, P < 0.05), but not with albuminuria or cystatin C. In 42 patients the different biochemical variables were again determined after 1 year, finding that in the 13 normotensive patients with normoalbuminuria there had been a significant decrease in the concentration of cystatin C (P < 0.05), and a significant increase in the urinary excretion of albumin and Hex B isoenzyme (P < 0.05). By the other hand, in the other 29 patients with micro- or macroalbuminuria and hypertension, no significant differences were found., Conclusion: The results point toward an important participation of tubular damage in the pathogenesis of this disease. It may also be suggested that in normotensive and normoalbuminuric ADPKD patients, a gradual increase of glomerular filtration would be produced. After the start of hypertension and microalbuminuria, the glomerular filtration rate (GFR) would decrease progressively, although more slowly.

Background: It has been suggested that the activity of beta-N-acetylhexosaminidase (Hex) in seminal plasma may be used as a biochemical marker of azoospermia. The purpose of our study was to evaluate this hypothesis using a thermodynamic procedure developed to determine total Hex activity and that of its isoenzymes in this biological fluid., Methods: Using the substrate 3,3'-dichlorophenolsulphoftaleinil N-acetyl-beta-D-glucosaminide, a highly significant difference (p<0.001) is found between the activation energy of Hex A (41.5 kJ/mol) and of Hex B (72.3 kJ/mol), making it possible to determine the activity of these isoenzymes from the apparent activation energy of the total Hex in seminal plasma., Results: A significant difference between the normozoospermic and azoospermic groups was only found for Hex A isoenzyme activity (p<0.05), although with considerable overlapping between the values of both groups. Significant partial correlations were found for the total Hex, Hex A and Hex B activities with the immobile spermatozoa count (p<0.01) and for total Hex and Hex B with the dead spermatozoa count (p<0.05). In turn, Hex A had a significant partial correlation with the live spermatozoa count (p<0.05); however, Hex activity in seminal plasma of acromosomal origin appears to be of little importance in quantitative terms., Conclusions: It was not possible to confirm that total Hex activity in seminal plasma, or even of its isoenzymes Hex A and Hex B, is a suitable biochemical marker of azoospermia (efficiency< or =67%). The thermodynamic procedure described may be a useful alternative for the study of the Hex enzyme heterogeneity in spermatozoa.

In patients with hypoalbuminemia, the total serum concentration of valproic acid may offer poor clinical information; however, very few clinical laboratories routinely analyze the free concentration of the drug. The aim of this study was to design a procedure to normalize the total concentration of valproic acid according to the level of serum albumin and using previously published free fraction values. In 121 adult patients, with albumin levels of 18 - 41 g/L, the total concentration of valproic acid was normalized using the derived equation: C(N) = alpha(H)C(H)/6.5, where alpha(H) is the free fraction of the drug corresponding to the patient's particular albuminemia and C(H) is the total concentration of valproic acid. The value of 6.5 corresponds to the free fraction of the drug for a serum albumin of 42 g/L (percentile 50 of the reference range). For total concentrations lower than 75 mg/L, the predicted normalized valproic acid concentrations were reasonably concordant with the observed normalized concentrations calculated using the data from a protein-binding study. In a significant number of cases, subtherapeutic concentrations of the drug became therapeutic and even supratherapeutic when corrected according to the albumin levels. Furthermore, cases with therapeutic drug concentrations frequently became supratherapeutic when normalized. The limitations and clinical applications of the proposed formula for normalizing the total concentration of valproic acid are presented. It is concluded that it may be useful for the posological management of hypoalbuminemic patients when the free concentration of the drug is not available, and decisions have to be made based on the total serum concentration.

Recently, the possible interference of hematocrit on the results of the Abbott Tacrolimus II microparticle enzyme immunoassay (MEIA) has been described, although its significance in clinical practice has not been established as yet. The aim of our study was the evaluation of the significance of this analytical interference in therapeutic tacrolimus monitoring. In 1121 cases selected at random over a 9-month period from kidney (n=379) and liver (n=742) transplant patients, an estimation was made of errors caused by the hematocrit in the results provided by the Tacrolimus II MEIA. In accordance with the available data, it was assumed that an error may be produced beyond the range of hematocrit values from 30% to 40%, either positive or negative respectively, of 3% per unit of hematocrit. The acceptance criterion for accuracy was no more than 15% of deviation (error) with respect to the experimental concentration of tacrolimus. In 160 cases (14.3%) the results of the Tacrolimus II MEIA would not be acceptable due to hematocrit-dependent errors, both with positive (hematocrit <25%) in 108 cases (9.7%) and negative values (hematocrit >45%) in 52 cases (4.6%). The obtained results demonstrate the practical interest of the subject, although additional studies are required in order to validate our approach to the clinical significance of this hematocrit-dependent interference in the Tacrolimus MEIA.

Objectives: Significant decreases in the serum concentration of pyridoxal-5' -phosphate (PLP) have been described in epileptic patients treated with anticonvulsant drugs. This would be expected to lead to a decrease in the sensitivity of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) for the detection of hepatocellular damage in these patients if optimized methods with coenzyme supplementation are not used. The aim of our study was to evaluate this hypothesis., Design and Methods: The serum activities of AST and ALT (with and without the addition of PLP) were determined in a group of 90 adult epileptic patients (56 male, 34 female) undergoing chronic treatment polytherapy with phenobarbital, phenytoin, carbamazepine, and valproic acid. As a control group, 49 clinically healthy individuals were studied with a similar distribution for age and sex., Results: Supplementation with PLP produced an activation of AST and ALT in both the control and patient groups with a highly significant correlation between the enzyme activities with and without the addition of PLP (r > or = 0.956, P < 0.001). The differences between the control and patient groups for the PLP activation of both aminotransferases were not clinically significant. The increases in AST (9%) and ALT (28%) in the patient group compared to the control group were lower than those found for alcohol dehydrogenase (ADH, 82%) and alpha-glutathione S-transferase (alphaGST, 76%)., Conclusions: It does not appear that in the epileptic patients studied the in vitro addition of PLP increased the diagnostic sensitivity of AST and ALT for hepatocellular injury. The lower responses of both aminotransferases to the action of anticonvulsant drugs in relation to other cytosolic enzymes may be due to the preferred periportal localization of AST and ALT in the hepatic lobe.